The National Credit Union Administration (NCUA)
Credit unions can do everything a bank can do. They offer checking and savings accounts, ATM cards, and even loans — often at better interest rates than conventional banks. The main difference is that credit unions are not-for-profit institutions owned by their account holders, aka "members." Usually to qualify for membership, you need to live in the same geographic area as the other members, work for the same company, attend the same college, or share other community bonds.
Just like banks, however, credit unions can fail. And when credit unions go bust, the National Credit Union Administration (NCUA) comes to the rescue. Much like the FDIC, the NCUA insures credit union deposits up to $250,000. If the NCUA can't turn around a credit union's finances, it liquidates the credit union and returns all assets to the members.
If an account refund check comes back as undeliverable, though, the clock starts ticking. The NCUA only guarantees full payment of undeliverable accounts up to 18 months after liquidation [source: NCUA]. If you wait too long to claim unreturned funds, you could lose them for good. The NCUA doesn't have a searchable database, but you can look up your name on this updated list.